https://sourceware.org/bugzilla/show_bug.cgi?id=34811
Bug ID: 34811
Summary: GNU ld m68hc11 --relax far-branch rewrite dereferences
a NULL section-contents pointer
Product: binutils
Version: 2.46
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: ld
Assignee: unassigned at sourceware dot org
Reporter: basavesh.shivakumar at wsu dot edu
Target Milestone: ---
Created attachment 17131
--> https://sourceware.org/bugzilla/attachment.cgi?id=17131&action=edit
repro
I'm reporting this bug on behalf of my team: Ananta Srikar Puranam, Emily West,
Dr. Swarn Priya, Dr. Peng Gao and Dr. Basavesh Ammanaghatta Shivakumar.
Summary
=======
GNU ld linking a m68hc11 static executable with --relax, given the exact object
the m68hc11 assembler emits for a far conditional branch (bne .+3; jmp
target_fn, R_M68HC11_RL_JUMP + R_M68HC11_16), runs the far-to-near branch
relaxation in m68hc11_elf_relax_section, which calls
m68hc11_elf_relax_delete_bytes (bfd/elf32-m68hc11.c:1151) before the section
this_hdr.contents is cached; the memmove dereferences a NULL contents pointer.
Released GNU ld 2.47 and a plain master build SIGSEGV (exit 139); an ASan+UBSan
build of master ab7102f76c08 reports a NULL-pointer access at
elf32-m68hc11.c:1151. The same object linked without --relax, and a relaxable
near-call object linked with --relax, link cleanly.
Reproduction
============
1. Download and extract
`bfd-m68hc11-relax-far-branch-null-deref-reproducer.tar.gz`.
2. Run the following command with an ld.bfd or all-target `ld-new` binary that
supports the emulation used by the reproducer:
LD=/path/to/ld-new sh repro.sh
The archive contains the fixed input files, independent controls, helper
scripts needed by `repro.sh`, and their checksums. The script uses a temporary
directory and does not modify the source tree.
Observed result
===============
GNU ld linking a m68hc11 static executable with --relax, given the exact object
the m68hc11 assembler emits for a far conditional branch (bne .+3; jmp
target_fn, R_M68HC11_RL_JUMP + R_M68HC11_16), runs the far-to-near branch
relaxation in m68hc11_elf_relax_section, which calls
m68hc11_elf_relax_delete_bytes (bfd/elf32-m68hc11.c:1151) before the section
this_hdr.contents is cached; the memmove dereferences a NULL contents pointer.
Released GNU ld 2.47 and a plain master build SIGSEGV (exit 139); an ASan+UBSan
build of master ab7102f76c08 reports a NULL-pointer access at
elf32-m68hc11.c:1151. The same object linked without --relax, and a relaxable
near-call object linked with --relax, link cleanly.
Expected result
===============
GNU ld should either produce the correct output or reject the input with a
normal diagnostic. It should not crash, hang, execute undefined behavior, read
outside an input-derived allocation, or produce the described malformed
output.
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